This genetic toxicity testing contract has supported the overall mission of NTP to provide detailed toxicological profiles, including potential for carcinogenicity, of compounds of interest for 30 years. Assessment of genetic damage, an important factor in the etiology of cancer as well as neurodegenerative diseases such as ALS, neurological conditions such as autism, aging, birth defects such as Down syndrome, mitochondrial diseases, and other adverse human health effects, is a critical component of any in-depth toxicological profile of a chemical or product. This Genetic Toxicity Testing contract provides this type of information to NTP using standard tests as well as innovative protocols when necessary. The capabilities of the contract are continuously updated to remain current and compatible with international guidelines for conducting these kinds of tests. Testing systems employed include both in vitro (animal cell-based and bacterial) and in vivo (rats and mice) assays. Three main tests are conducted routinely: in vitro bacterial mutagenicity assays, in vivo rodent peripheral blood micronucleus (MN) assays, and in vivo rodent DNA damage (Comet) assays in multiple tissues including, for example, liver, brain, stomach, kidney, and lung. In addition, in vitro MN assays have become increasingly used as a substitute for stand-alone in vivo rodent MN assays. During this past fiscal year, another animal mutation endpoint that holds promise for application in human clinical and biomonitoring studies in the future, has been investigated in the testing laboratory: the pig-a mutation assay (phosphatidylinositol glycan anchor biosynthesis, class A gene). Mutations in this gene are easily detected in red blood cell samples from laboratory rodents, and updated methods to streamline the assay have been developed, so that integration into existing toxicity tests can be more be accomplished. During the next fiscal year, we will attempt to multiplex this assay with the in vivo MN and Comet assays, increasing the genetic toxicity information that we obtain from test animals to provide an even more comprehensive profile of the genetic toxicity potential of a chemical. In addition to our cell-based and animal model studies, human blood samples provided by collaborators such as NIOSH and the NIEHS Clinical Research Unit may also be examined for specific genetic endpoints following an environmental exposure that is suspected to be capable of inducing genetic damage, or has been shown to do so in NTP animal studies. The number of studies of each type described above varies annually, depending on the needs of the NTP. For example, this past year, in a rapid response effort to the chemical spill in the Elk River in West Virginia, the genetic toxicity testing contract laboratory assessed peripheral blood samples from rats treated with 3 of the main constituents of the spilled product for chromosomal damage and also tested 9 constituents (both major and minor constituents) in bacterial mutagenicity assays (Ames tests). These tests were in addition to the usual number (10 ? 12) of bacterial mutagenicity studies planned annually. The laboratory has also been generating mutagenicity data on a number of herbal products under study by the NTP, and has been conducting innovative in vitro chromosomal damage studies with one particular widely used product, to investigate mode of action for the chromosomal damage observed with this herbal product in NTP animal studies.